Polyamides have excellent heat resistance and chemical resistance and are generally used as engineering plastics. The polyamides, however, have high water-absorbing properties and reduce elastic modulus or show bad dimensional stability when they absorb water.
To compensate for such defects of the polyamides, it has been a conventional practice to blend the polyamides with polypropylene that is a non-polar resin having low water absorbability and excellent heat resistance. They are immiscible by simple mixing such as kneading, and therefore a compatibilizer is used in the mixing.
For example, Patent Document 1 discloses automobile connectors which are molded from a polyamide composition containing a polyamide, a polypropylene, a modified polymer obtained by introducing an acid anhydride group into polypropylene and/or a vinyl aromatic compound/olefin copolymer, and an olefin oligomer or a vinyl aromatic compound/olefin copolymerized oligomer which is liquid and contains an acid anhydride group.
Patent Document 1 describes that the polyamide compositions obtained by adding the modified propylene resin and the oligomer to polyamide and polypropylene achieve improved heat resistance and dimensional stability. However, the polyamide compositions of Patent Document 1 essentially contain the oligomer having an acid anhydride group and therefore the polyamide compositions have room for improvement in properties such as strength.
Further, Patent Document 2 discloses thermoplastic polypropylene-polyamide forming materials that contain at least a polypropylene homopolymer and/or a polypropylene copolymer, a polyamide, and an olefinically unsaturated carboxylic acid and/or an olefinically unsaturated carboxylic acid derivative.
Patent Document 2 describes that the thermoplastic polypropylene-polyamide forming materials possess high toughness, rigidity and thermo-molding stability. However, the thermoplastic polypropylene-polyamide forming materials of Patent Document 2 have room for improvement in properties such as compatibility between the polypropylene and the polyamide.
Furthermore, Patent Document 3 discloses polyamide/polyolefin resin compositions containing a polyamide resin, a polypropylene resin and a modified polyolefin resin.
Patent Document 3 describes that the polyamide/polyolefin resin compositions have high impact resistance and weld strength. The modified polyolefin resins of Patent Document 3 are obtained by adding an acid anhydride to a mixture of a polypropylene resin and a polyethylene resin. The modified resins are poor in compatibility between the polyamide resin and the polypropylene resin and therefore have room for improvement in properties such as appearance and tensile elongation.    Patent Document 1: JP-A-H01-311580    Patent Document 2: JP-A-H03-109452    Patent Document 3: JP-A-H04-252264